Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $48.53   10.832%   $53.7868   $53.79   $53.80   $53.80  
  Purchase #2 $239.94   11.543%   $267.6363   $267.64   $267.65   $267.60  
  Purchase #3 $19.64   9.351%   $21.4765   $21.48   $21.50   $21.50  
  Purchase #4 $172.84   12.200%   $193.9265   $193.93   $193.95   $193.90  
  Purchase #5 $64.48   4.544%   $67.41   $67.41   $67.40   $67.40  
  Purchase #6 $192.41   10.166%   $211.9704   $211.97   $211.95   $212.00  
  Purchase #7 $245.40   8.518%   $266.3032   $266.30   $266.30   $266.30  
  7 purchase totals = $983.24       $1,082.5097   $1,082.52   $1,082.55   $1,082.50